Flow features for self-cleaning concentric tubular electrochemical cells

ABSTRACT

Self-cleaning electrochemical cells, systems including self-cleaning electrochemical cells, and methods of operating self-cleaning electrochemical cells are disclosed. The self-cleaning electrochemical cell can include a plurality of concentric electrodes disposed in a housing, for example, a cathode and an anode, a fluid channel defined between the concentric electrodes, a separator residing between the concentric electrodes, first and second end caps coupled to respective ends of the housing, and an inlet cone. The separators may be configured to localize the electrodes and dimensioned to minimize a zone of reduced velocity occurring downstream from the separator. The end caps and inlet cone may be dimensioned to maintain fully developed flow and minimize pressure drop across the electrochemical cell.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application Ser. No. 62/485,539, titled “NOVEL FLOW FEATURESFOR SELF-CLEANING CONCENTRIC TUBULAR ELECTROCHEMICAL CELLS,” filed onApr. 14, 2017, which is incorporated herein by reference in its entiretyfor all purposes.

FIELD OF TECHNOLOGY

Aspects and embodiments disclosed herein are generally directed toelectrochemical devices, and more specifically, to electrochlorinationcells and devices, methods of operating same, and systems utilizingsame.

SUMMARY

In accordance with one aspect, there is provided a self-cleaningelectrochemical cell. The self-cleaning electrochemical cell maycomprise a cathode and an anode disposed concentrically in a housingabout a central axis of the housing. The self-cleaning electrochemicalcell may comprise a fluid channel defined between the cathode and theanode and extending substantially parallel to the central axis. Theself-cleaning electrochemical cell may comprise a separator residingbetween the cathode and the anode and configured to maintain the fluidchannel, the separator having a height which maintains a width of thefluid channel. The separator may be dimensioned to maintain a zone ofreduced velocity within the fluid channel downstream of the separator tobe less than a predetermined length. The separator may be dimensioned tomaintain an electrolyte solution velocity deviation from mean to bewithin ±18% of an average flow velocity of the electrolyte solutionthrough the fluid channel.

In some embodiments, the velocity deviation from mean at thepredetermined length may be less than ±5% of the average flow velocityof the electrolyte solution. The velocity deviation from mean at thepredetermined length may be less than ±2% of the average flow velocityof the electrolyte solution.

The predetermined length may be less than about 120 mm for seawaterflowing through the fluid channel at an average flow velocity of between2 and 2.5 m/s. The predetermined length may be less than about 60 mm.

In accordance with certain embodiments, the separator may comprise aring and a plurality of projections extending from the ring. Theprojections may have a height which maintains the width of the fluidchannel. A number of projections and a length and width of eachprojection may be selected to maintain the zone of reduced velocity atless than the predetermined length.

The self-cleaning electrochemical cell may contain a plurality ofcathodes and a plurality of anodes arranged concentrically about thecentral axis of the housing. A respective one of a plurality of fluidchannels may be defined between each adjacent cathode and anode. Eachfluid channel may extend substantially parallel to the central axis.

The self-cleaning electrochemical cell may include a plurality ofseparators. Each separator may be configured to maintain a respectiveone of the plurality of fluid channels, the plurality of separators mayeach include a ring and a plurality of projections extending from thering. In some embodiments, the separator may be configured to mate withat least one of the cathode and the anode.

In accordance with another aspect, there is provided a system comprisinga self-cleaning electrochemical cell and a source of the electrolytesolution. The self-cleaning electrochemical cell may have an inlet andan outlet fluid communication with the fluid channel. The source of theelectrolyte solution may have an outlet fluidly connectable to the inletof the self-cleaning electrochemical cell and configured to deliver theelectrolyte solution at an average flow velocity through the fluidchannel of 2 m/s or greater. The self-cleaning electrochemical cell maybe configured to produce a product compound from the electrolytesolution and to output a product solution comprising the productcompound. The self-cleaning electrochemical cell may be fluidlyconnectable to a point of use through the outlet.

In some embodiments, the source of the electrolyte solution may compriseat least one of seawater, brackish water, and brine. The system mayinclude a plurality of self-cleaning electrochemical cells arranged inseries.

In accordance with another aspect, there is provided a self-cleaningelectrochemical cell comprising a cathode and an anode disposedconcentrically in a housing about a central axis of the housing, a fluidchannel defined between the cathode and the anode and extendingsubstantially parallel to the central axis, first and second end caps,and an inlet cone. The first end cap may be coupled to a first end ofthe housing and the second end cap may be coupled to a second end of thehousing. Each of the first end cap and the second end cap may include asubstantially centrally located aperture and a fluid conduit in fluidcommunication with the fluid channel. The fluid conduit of the first endcap may comprise a zone of a first radius and a zone of a second radiusgreater than the first radius. The inlet cone may be disposed within thefluid conduit of the first end cap and configured to define a flow pathfor an electrolyte solution into the fluid channel. The zone of thesecond radius may have a length selected to maintain fully-developedflow through the flow path.

The zone of the second radius may have a length between 1 and 10 times ahydraulic diameter of the flow path. The fluid conduit of the first endcap may be dimensioned to maintain an inlet pressure of the electrolytesolution below about 120 kPa. The inlet cone may be dimensioned tomaintain a pressure drop within the self-cleaning electrochemical cellbetween 0 and 19 kPa.

The inlet cone maybe a right circular cone having an apex angle ofbetween 20° and 90°. The inlet cone may be a right circular cone havingan apex angle of between 40° and 60°. The self-cleaning electrochemicalcell may comprise an outlet frustrum disposed within the fluid conduitof the second end cap and configured to define a flow path for theelectrolyte solution from the fluid channel out of the self-cleaningelectrochemical cell.

In accordance with another aspect, there is provided a system comprisinga self-cleaning electrochemical cell and a source of the electrolytesolution. The self-cleaning electrochemical cell may have an inlet andan outlet. The source of the electrolyte solution may have an outletfluidly connectable to the substantially centrally located aperture ofthe first end cap and configured to deliver the electrolyte solution atan average flow velocity through the fluid channel of 2 m/s or greater.The self-cleaning electrochemical cell may be configured to produce aproduct compound from the electrolyte solution and to output a productsolution comprising the product compound. The self-cleaningelectrochemical cell may be fluidly connectable to a point of usethrough the substantially centrally located aperture of the second endcap.

In some embodiments, the source of the electrolyte solution may compriseat least one of seawater, brackish water, and brine. The system mayinclude a plurality of self-cleaning electrochemical cells arranged inseries.

In accordance with another aspect, there is provided a self-cleaningelectrochemical cell comprising a cathode and an anode disposedconcentrically in a housing about a central axis of the housing, a fluidchannel defined between the cathode and the anode and extendingsubstantially parallel to the central axis, and a separator residingbetween the cathode and the anode. The separator may be configured toallow passage of an electrolyte solution through the fluid channel. Theseparator maybe dimensioned to maintain the fluid channel and have anaqualined configuration.

The separator may include a ring and a plurality of projectionsextending from the ring. Each projection may have a height whichmaintains the width of the fluid channel and a width sufficient tomaintain the fluid channel. In some embodiments, each projection canhave a width between 0.5 and 2 times the height and a length greaterthan the width. Each projection may have an aqualined configuration. Theplurality of projections may be substantially evenly spaced apart on thering.

In some embodiments, the separator may be dimensioned to have across-sectional area between about 10% and about 35% of a flow area ofthe fluid channel. The separator may be configured to mate with at leastone of the cathode and the anode.

In accordance with another aspect, there is provided a system comprisinga self-cleaning electrochemical cell and a source of the electrolytesolution. The self-cleaning electrochemical cell may have an inlet andan outlet in fluid communication with the fluid channel. The source ofthe electrolyte solution may have an outlet fluidly connectable to theinlet of the self-cleaning electrochemical cell and configured todeliver the electrolyte solution at an average flow velocity through thefluid channel of 2 m/s or greater. The self-cleaning electrochemicalcell may be configured to produce a product compound from theelectrolyte solution and to output a product solution comprising theproduct compound. The self-cleaning electrochemical cell may be fluidlyconnectable to a point of use through the outlet.

In some embodiments, the source of the electrolyte solution may compriseat least one of seawater, brackish water, and brine. The system mayinclude a plurality of self-cleaning electrochemical cells arranged inseries.

In another aspect, there is provided a method of operating anelectrochemical system. The method may comprise providing theself-cleaning electrochemical cell, introducing the electrolyte solutioninto the self-cleaning electrochemical cell at an average flow velocitythrough the fluid channel of about 2 m/s or greater, applying a currentacross the anode and the cathode at a voltage sufficient to generate aproduct compound from the electrolyte solution in the self-cleaningelectrochemical cell, and continuously operating the electrochemicalsystem for a predetermined period of time. The method may comprisecontinuously operating the electrochemical system for at least 6 months.In some embodiments, the method may comprise providing a plurality ofself-cleaning electrochemical cells and fluidly connecting the pluralityof self-cleaning electrochemical cells in series.

In accordance with another aspect, there is provided a self-cleaningelectrochemical cell comprising a plurality of electrodes disposed in ahousing, a fluid channel, and a plurality of concentric separators. Theplurality of electrodes may comprise concentric electrodes disposedabout a central axis of the housing and consecutive electrodes disposedalong a length of the housing. The fluid channel may be defined betweenconcentric electrodes and extend substantially parallel to the centralaxis. Each concentric separator from the plurality of concentricseparators may be positioned between consecutive electrodes andconfigured to mate with at least one of the consecutive electrodes. Theplurality of concentric separators may be configured to maintainconcentricity of the consecutive electrodes.

In some embodiments, each of the concentric separators comprises aplurality of contiguous rings. A width of a gap between an adjacent twoof the plurality of contiguous rings may be dimensioned to maintain azone of reduced velocity within the fluid channel to be less than apredetermined length.

The length of the zone of reduced velocity may be defined by an area inwhich an average electrolyte solution flow velocity is at least 2% lessthan an average flow velocity of the electrolyte solution through thefluid channel. In some embodiments, the length of the zone of reducedvelocity may be defined by an area in which an average electrolytesolution flow velocity is at least 5% less than an average flow velocityof the electrolyte solution through the fluid channel. In accordancewith certain embodiments, the width of the gap between adjacent two ofthe plurality of contiguous rings may be 1.60 times or less a width ofat least one of the plurality of contiguous rings. In some embodiments,at least one ring of the plurality of contiguous rings may include aplurality of projections extending from the at least one ring.

In accordance with another aspect, there is provided a system comprisinga self-cleaning electrochemical cell and a source of the electrolytesolution. The source of the electrolyte solution may have an outletfluidly connectable to the inlet of the housing and configured todeliver the electrolyte solution at an average flow velocity through thefluid channel of 2 m/s or greater. The self-cleaning electrochemicalcell may be configured to produce a product compound from theelectrolyte solution and to output a product solution comprising theproduct compound. The self-cleaning electrochemical cell may be fluidlyconnectable to a point of use through the outlet.

In some embodiments, the source of the electrolyte solution may compriseat least one of seawater, brackish water, and brine. The system mayinclude a plurality of self-cleaning electrochemical cells arranged inseries.

In another aspect, there is provided a method of operating anelectrochemical system. The method may comprise providing theself-cleaning electrochemical cell, introducing an electrolyte solutioninto the self-cleaning electrochemical cell at an average flow velocitythrough the fluid channel of about 2 m/s or greater, applying a currentacross the plurality of electrodes at a voltage sufficient to generate aproduct compound from the electrolyte solution in the self-cleaningelectrochemical cell, and continuously operating the electrochemicalsystem for a predetermined period of time. The method may comprisecontinuously operating the electrochemical system for at least 6 months.In some embodiments, the method may comprise providing a plurality ofself-cleaning electrochemical cells and fluidly connecting the pluralityof self-cleaning electrochemical cells in series.

The disclosure contemplates all combinations of any one or more of theforegoing aspects and/or embodiments, as well as combinations with anyone or more of the embodiments set forth in the detailed description andany examples.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1A is an isometric view of an embodiment of a concentric tubeelectrochemical cell;

FIG. 1B is a cross-sectional view of the concentric tube electrochemicalcell of FIG. 1A;

FIG. 1C includes an elevational view and a cross-sectional view of theconcentric tube electrochemical cell of FIG. 1A;

FIG. 1D is an alternate isometric view of the concentric tubeelectrochemical cell of FIG. 1A;

FIG. 2A illustrates current flow through an embodiment of a concentrictube electrochemical cell;

FIG. 2B illustrates current flow through another embodiment of aconcentric tube electrochemical cell;

FIG. 2C illustrates current flow through another embodiment of aconcentric tube electrochemical cell;

FIG. 3A is a cross-sectional view of an electrochemical cell, accordingto one embodiment;

FIG. 3B is a magnified cross-sectional view of a portion of theelectrochemical cell of FIG. 3A;

FIG. 3C is a cross-sectional view of the exemplary electrochemical cellof FIG. 3A;

FIG. 4 is a contour map of the velocity profile down a fluid channel ofan electrochemical cell, according to some embodiments;

FIG. 5 is a contour map of the velocity profile down a fluid channel ofan electrochemical cell, according to an alternate embodiment;

FIG. 6A is an isometric view of a separator, according to oneembodiment;

FIG. 6B is an elevational view of a projection on a separator, accordingto one embodiment;

FIG. 6C is a plan view of a projection on a separator, according to oneembodiment;

FIG. 6D is an isometric view of a projection on a separator, accordingto one embodiment;

FIG. 7A is an isometric view of separators positioned between electrodetubes, according to one embodiment;

FIG. 7B is an elevational view of the separators and electrodes of FIG.7A;

FIG. 7C is an isometric view of a separator, according to oneembodiment;

FIG. 7D contains elevational views of the separator of FIG. 7C;

FIG. 8A is an elevational view of an electrochemical cell, according toone embodiment;

FIG. 8B is a cross-sectional view of the electrochemical cell of FIG.8A;

FIG. 9A is a plan view from the top of an end cap, according to oneembodiment;

FIG. 9B is a plan view from the bottom of the end cap of FIG. 9A;

FIG. 9C is an elevational view of the end cap of FIG. 9A;

FIG. 9D is a cross-sectional view of the end cap of FIG. 9A;

FIG. 10A is a cross-sectional view of a portion of an electrochemicalcell, according to one embodiment;

FIG. 10B is an exploded view of the portion of the electrochemical cellof FIG. 10A;

FIG. 11A is a cross-sectional view of a portion of an electrochemicalcell, according to one embodiment;

FIG. 11B is an isometric view of a portion of an electrochemical cell,according to another embodiment;

FIG. 12 is a contour map of pressure drop across an electrochemicalcell, according to one embodiment;

FIG. 13A is a contour map of inlet pressure in an inlet end cap of anelectrochemical cell, according to one embodiment;

FIG. 13B is an alternate contour map of inlet pressure in an inlet endcap of an electrochemical cell, according to another embodiment;

FIG. 13C is an alternate contour map of inlet pressure in an inlet endcap of an electrochemical cell, according to another embodiment;

FIG. 14A is a collection of contour maps of inlet pressure in an inletend cap of an electrochemical cell with varying inlet cone embodiments;

FIG. 14B is a graph of pressure drop vs. cone angle for the inlet coneembodiments of FIG. 14A;

FIG. 15A is a cross-sectional view of an electrochemical cell, accordingto one embodiment;

FIG. 15B is a contour map of outlet pressure in an outlet cap of anelectrochemical cell with an outlet frustrum, according to oneembodiment;

FIG. 16 is an isometric view of a portion of an electrochemical cell,according to one embodiment;

FIG. 17A is an isometric view of a portion of an electrochemical cell,according to one embodiment;

FIG. 17B is an isometric view of another portion of the electrochemicalcell of FIG. 17A;

FIG. 17C is an isometric view of another portion of the electrochemicalcell of FIG. 17A;

FIG. 18A is an isometric view of a portion of an electrochemical cell,according to one embodiment;

FIG. 18B is a plan view of the portion of the electrochemical cell ofFIG. 18A;

FIG. 19A is an exploded view of a separator, according to oneembodiment;

FIG. 19B is a plan view of the separator of FIG. 19A;

FIG. 19C is a cross-section view of the separator of FIG. 19A;

FIG. 20A is an isometric view of a portion of a separator, according toone embodiment;

FIG. 20B is an elevational view of the separator of FIG. 20A;

FIG. 20C is a cross-section view of the separator of FIG. 20A;

FIG. 21A is an isometric view of a separator, according to oneembodiment;

FIG. 21B is an elevational view of the separator of FIG. 21A;

FIG. 21C is a cross-sectional view of the separator of FIG. 21A;

FIG. 21D is an exploded view of the separator of FIG. 21A;

FIG. 22 is a graph of velocity deviation from mean downstream from aseparator, according to one embodiment;

FIG. 23A is a cross-sectional view of an electrochemical cell, accordingto one embodiment;

FIG. 23B is a magnified view of a portion of the electrochemical cell ofFIG. 23A;

FIG. 23C is an elevational view of an electrical connector of anelectrochemical cell, according to one embodiment;

FIG. 23D is an isometric view of the electrical connector of FIG. 23C;

FIG. 24A is an elevational view of an electrical connector, according toone embodiment;

FIG. 24B is a magnified view of a portion of the electrical connector ofFIG. 24A;

FIG. 24C is a side view of a portion of the electrical connector of FIG.24A;

FIG. 25A is an isometric view of a portion of an electrochemical cell,according to one embodiment;

FIG. 25B includes contour maps of current distribution across theportion of the electrochemical cell of FIG. 25A;

FIG. 25C is a contour map of temperature around an electrical connectorof an electrochemical cell, according to one embodiment;

FIG. 25D is a contour map of velocity downstream from an electricalconnector of an electrochemical cell, according to one embodiment;

FIG. 26A is an elevational view of an electric connection of anelectrochemical cell, according to one embodiment;

FIG. 26B is an elevational view of an alternate electric connection ofan electrochemical cell, according to another embodiment;

FIG. 26C is a top view contour map of current distribution around theelectric connections of FIG. 26A (left) and FIG. 26B (right);

FIG. 26D is a side view contour map of current distribution around theelectric connections of FIG. 26A (left) and FIG. 26B (right);

FIG. 27A is an elevational view of an electric connection of anelectrochemical cell, according to one embodiment;

FIG. 27B is an elevational view of an alternate electric connection ofan electrochemical cell, according to another embodiment;

FIG. 27C is a top view contour map of current distribution around theelectric connections of FIG. 27A (left) and FIG. 27B (right);

FIG. 27D is a side view contour map of current distribution around theelectric connections of FIG. 27A (left) and FIG. 27B (right);

FIG. 28A is a contour map of flow velocity through an electrochemicalcell including the electrical connector of FIG. 26A;

FIG. 28B is a contour map of flow velocity through an electrochemicalcell including the electrical connector of FIG. 26B;

FIG. 28C is a contour map of flow velocity through an electrochemicalcell including the electrical connector of FIG. 27A;

FIG. 28D is a contour map of flow velocity through an electrochemicalcell including the electrical connector of FIG. 27B;

FIG. 29A is an isometric view of an electrical connector and separatorassembly of an electrochemical cell, according to one embodiment;

FIG. 29B is a plan view of the electrical connector and separatorassembly of FIG. 29A;

FIG. 30 includes contour maps of flow velocity through anelectrochemical cell, according to one embodiment;

FIG. 31 includes contour maps of flow velocity through anelectrochemical cell, according to one embodiment; and

FIG. 32 includes contour maps of flow velocity through anelectrochemical cell, according to one embodiment.

DETAILED DESCRIPTION

Aspects and embodiments disclosed herein are not limited to the detailsof construction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. Aspects andembodiments disclosed herein are capable of being practiced or of beingcarried out in various ways. This disclosure describes variousembodiments of electrochlorination cells and electrochlorinationdevices, however, this disclosure is not limited to electrochlorinationcells or devices and the aspects and embodiments disclosed herein areapplicable to electrolytic and electrochemical cells used for any one ofmultiple purposes.

Electrochemical devices based on chemical reactions at electrodes arewidely used in industrial and municipal implementations. Examples ofreactions include:

Electrochlorination with generation of sodium hypochlorite from sodiumchloride and water:

Reaction at anode: 2Cl⁻→Cl₂+2e⁻

Reaction at cathode: 2Na⁺+2H₂O+2e⁻→2NaOH+H₂

In solution: Cl₂+2OH⁻→ClO⁻+Cl⁻+H₂O

Overall reaction: NaCl+H₂O→NaOCl+H₂

Generation of sodium hydroxide and chlorine from sodium chloride andwater, with a cation exchange membrane separating the anode and thecathode:

Reaction at anode: 2Cl⁻→Cl₂+2e⁻

Reaction at cathode: 2H₂O+2e⁻→2OH⁻+H₂

Overall reaction: 2NaCl+2H₂O→2NaOH+Cl₂+H₂

Vanadium redox battery for energy storage, with a proton permeablemembrane separating the electrodes:

During charging:

Reaction at 1st electrode: V³⁺+e⁻→V²⁺

Reaction at 2nd electrode: V⁴⁺→V⁵⁺+e⁻

During discharging:

Reaction at 1st electrode: V²⁺→V³⁺+e⁻

Reaction at 2nd electrode: V⁵⁺+e⁻→V⁴⁺

Electrochlorination cells can be used in marine, offshore, municipal,industrial and commercial implementations. The design parameters ofelectrochemical devices, for example, inter-electrode spacing, thicknessof electrodes and coating density, electrode areas, methods ofelectrical connections, etc. can be optimized for differentimplementations.

Removal of H₂ gas generated at the cathodes is a major challenge in thedesign of electrochemical devices and of the overall system. The gasmust be safely vented at either selected locations in the piping or atproduct tanks. In some embodiments, an oxidant may be introduced tomitigate H₂ gas generation, optionally by generating H₂O₂.

Aspects and embodiments disclosed herein are generally directed toelectrochemical devices to generate disinfectants such as sodiumhypochlorite. The terms “electrochemical device” and “electrochemicalcell” and grammatical variations thereof are to be understood toencompass “electrochlorination devices” and “electrochlorination cells”and grammatical variations thereof.

As disclosed herein, aspects and embodiments relate to concentrictubular electrochemical cells (CTE). FIG. 1A shows an exemplaryelectrochemical cell 100 with concentric tubes disposed within a housing116. The inner surface of the outer tube and the outer surface of theinner tube include the active electrode areas. As seen in FIG. 1B, feedelectrolyte solution flows between concentric tubes 102, 104 through alength of the electrochemical cell 100. A flow channel is created by agap between concentric tubes, as shown in FIG. 1D.

The gap between the electrodes in this exemplary embodiment isapproximately 3.5 mm. For certain applications (for example, marine andoffshore applications) with seawater as feed, the liquid velocitythrough the fluid channel can be greater than 2.0 m/s, for example, onthe order of 2.1 m/s, up to 3 m/s, up to 3.5 m/s, up to 6 m/s, or up to10 m/s, resulting in highly turbulent flow which reduces the potentialfor fouling and scaling on the electrode surfaces.

The electrochemical cell 100 can include end caps 106, 108 and a centercap 110 as shown in FIG. 1C. The electrochemical cell can include cones112, 114 as shown in FIGS. 1B and 1C. Cones 112, 114 may be provided onthe inner electrode to direct feed electrolyte solution towards the gapbetween concentric tubes 102, 104. Separators (alignment features) maybe positioned at one or more of the inlet, outlet, and center caps tomaintain an internal position of the concentric tubes and define thegap. End caps, cones, and separators have an impact on flow velocity andpressure drop through the electrochemical cell. Decreasing flow velocitycan increase the potential for fouling and scaling, resulting in agreater need for maintenance. In systems with multiple electrochemicalcells arranged in series, the pressure drop across each electrochemicalcell has a cumulative effect on the system. According to certainembodiments disclosed herein, one or more features may be designed toreduce the impact on flow velocity and pressure drop within theelectrochemical cell. Additionally, one or more features may be designedto simplify fabrication of electrochemical cells and their components.As disclosed herein, features may be designed by mathematical functionor freely generated. In some embodiments, features may be empiricallygenerated or designed using Computational Fluid Dynamics (CFD) software.

Aspects and embodiments disclosed herein are described as including oneor more electrodes. The term “metal electrodes” or grammaticalvariations thereof as used herein is to be understood to encompasselectrodes formed from, comprising, or consisting of one or more metals,for example, titanium, aluminum or nickel although the term “metalelectrode” does not exclude electrodes including of consisting of othermetals or alloys. In some embodiments, a “metal electrode” may includemultiple layers of different metals. Metal electrodes utilized in anyone or more of the embodiments disclosed herein may include a core of ahigh-conductivity metal, for example, copper or aluminum, coated with ametal or metal oxide having a high resistance to chemical attack byelectrolyte solutions, for example, a layer of titanium, platinum, amixed metal oxide (MMO), magnetite, ferrite, cobalt spinel, tantalum,palladium, iridium, silver, gold, or other coating materials.

“Metal electrodes” may be coated with an oxidation resistant coating,for example, but not limited to, platinum, a mixed metal oxide (MMO),magnetite, ferrite, cobalt spinel, tantalum, palladium, iridium, silver,gold, or other coating materials. Mixed metal oxides utilized inembodiments disclosed herein may include an oxide or oxides of one ormore of ruthenium, rhodium, tantalum (optionally alloyed with antimonyand/or manganese), titanium, iridium, zinc, tin, antimony, atitanium-nickel alloy, a titanium-copper alloy, a titanium-iron alloy, atitanium-cobalt alloy, or other appropriate metals or alloys. Anodesutilized in embodiments disclosed herein may be coated with platinumand/or an oxide or oxides of one or more of iridium, ruthenium, tin,rhodium, or tantalum (optionally alloyed with antimony and/ormanganese). Cathodes utilized in embodiments disclosed herein may becoated with platinum and/or an oxide or oxides of one or more ofiridium, ruthenium, and titanium. In some embodiments, both the anodeand cathode are coated similarly to allow for periodic polarity reversalof the electrodes. Electrodes utilized in embodiments disclosed hereinmay include a base of one or more of titanium, tantalum, zirconium,niobium, tungsten, and/or silicon. Electrodes for any of theelectrochemical cells disclosed herein can be formed as or from plates,sheets, foils, extrusions, and/or sinters.

The term “tube” as used herein includes cylindrical conduits, however,does not exclude conduits having other cross-sectional geometries, forexample, conduits having square, rectangular, oval, or obroundgeometries or cross-sectional geometries shaped as any regular orirregular polygon.

The terms “concentric tubes” or “concentric spirals” as used hereinincludes tubes or interleaved spirals sharing a substantially commoncentral axis, but does not exclude tubes or interleaved spiralssurrounding a substantially common axis that is not necessarily centralto each of the concentric tubes or interleaved spirals in a set ofconcentric tubes or interleaved spirals.

In accordance with an aspect, an electrochemical cell includesconcentric tube electrodes. At least some of the concentric tubeelectrodes may be mono-polar or bipolar. The inner tube electrode may bean anode having an oxidation resistant coating, for example, platinum orMMO. The outer tube electrode may have no coating, acting as a cathode.Alternatively, the inner tube electrode may act as a cathode and theouter tube electrode may act as an anode. In some embodiments, bothelectrodes are coated to allow for polarity reversal.

The electrodes in the exemplary embodiment may be mono-polar such thatcurrent passes through the electrolyte once per electrode. Each of theelectrodes may include a titanium tube. The anode electrical connectormay be in electrical communication with the outer tube electrode. Thecathode electrical connector may be in electrical communication with theinner tube electrode. If there is a middle tube electrode, it may be inelectrical communication with the inner tube electrode, outer tubeelectrode, or both. In some embodiments, the middle tube electrode maybe an anode having an oxidation resistant coating, for example, platinumor MMO, on both the inner and outer surface to make full use of thesurface. The middle tube anode may be surrounded by two electrodesacting as cathodes.

FIGS. 2A-2D show some possible exemplary arrangements of electrodes in aCTE electrochemical cell. FIG. 2A illustrates an exemplary arrangementin which current flows in one pass from the anode to the cathode. Bothelectrodes may be fabricated from titanium, with the anode coated withplatinum or a mixed metal oxide (MMO). Such electrodes are called“mono-polar.”

The electrodes in the exemplary embodiment may be bipolar such thatcurrent passes through the electrolyte more than once per electrode. Inan exemplary embodiment, one end of a bipolar tube electrode (in someembodiments about one half of the electrode) may be uncoated to functionas a cathode and the other end portion (in some embodiments about onehalf of the electrode) may be coated with an oxidation resistantcoating, for example, platinum or MMO, to function as an anode. Thebipolar tube electrode may be nested within the anode and cathode tubeelectrodes, each tube electrode surrounding one end portion of thebipolar electrode. An anode tube electrode and a cathode tube electrodehaving a common diameter may be laterally displaced along a length ofthe electrochemical cell. The bipolar tube electrode may be oriented toenable current to flow in two passes through electrolyte solutionpassing between the bipolar tube electrode, the anode tube electrode,and the cathode tube electrode.

By inserting additional bipolar tube electrodes and overlappingrespective anode tube electrodes and cathode tube electrodes such thatanode and cathode tube electrodes are provided on alternative sides of aplurality of bipolar tube electrodes along an axial direction throughthe electrochemical cell, the cell can be assembled to provide three ormore current passes, schematically similar to the multi-pass parallelplate electrode (PPE).

FIG. 2B illustrates an exemplary arrangement in which current flows intwo passes through the device with two outer electrodes and one innerelectrode. One of the outer electrodes is coated on the inside surface,for example, to serve as an anode; the other is uncoated. A portion ofthe outer surface of the inner electrode is coated, for example, to alsoserve as an anode, and the remaining portion is uncoated. Current flowsthrough the electrolyte from the coated outer electrode to the uncoatedportion of the inner electrode, along the inner electrode to the coatedportion, then finally back across the electrolyte to the uncoated outerelectrode. The inner electrode is also called a “bipolar” electrode.

FIG. 2C illustrates an arrangement in which current flows in multiplepasses through the device with multiple outer electrodes and one innerelectrode. By alternating cathode and anode portions and coating theelectrodes where necessary, current can flow back and forth through theelectrolyte in multiple passes. The number of passes can be scaled upaccordingly.

In accordance with an aspect, an electrochemical cell includes aplurality of concentric tube electrodes. In embodiments disclosed hereinincluding multiple anode or cathode tube electrodes, the multiple anodetube electrodes may be referred to collectively as the anode or theanode tube, and the multiple cathode tube electrodes may be referred tocollectively as the cathode or the cathode tube. In embodimentsincluding multiple anode and/or multiple cathode tube electrodes, themultiple anode tube electrodes and/or multiple cathode tube electrodesmay be collectively referred to herein as an anode-cathode pair.

The electrochemical cell can include, for example, three, four, or fiveconcentric tubes. In some embodiments, the electrochemical cell mayinclude three or four concentric tube electrodes, with two outer tubeelectrodes and one or two inner tube electrodes. A four tubeelectrochemical cell may work in a similar way to a three tubeelectrochemical cell, except that an electrolyte solution may flowthrough three fluid channels instead of two. The extra electrode tubemay provide an additional cathode electrode surface, anode electrodesurface, and fluid channel. Similarly, an electrochemical cell includingfive tube electrodes may include two outer tubes, three inner tubes, andfour fluid channels. The fifth electrode tube may provide yet anadditional cathode electrode surface, anode electrode surface, and fluidchannel. The number of tubes, the number of passes, and the electrodeconfiguration (mono-polar or bipolar) may vary. The number of tubes,number of passes, and electrode configuration may be selected based onthe desired use of the electrochemical cell.

Multi-tube electrode arrangements as disclosed herein progressivelyincrease active area per unit volume. With increasing number ofmulti-tubes used in electrochemical or electrochlorination cells anddevices including multiple concentric tube electrodes, the innermosttube diameter will become increasingly smaller with less active surfacearea per tube. However, the overall result is the multi-tube electrodewill have significantly more active surface when compared to other CTEelectrode devices.

As the term is used herein, an “active density” of an electrochemicalcell is defined as the ratio of the cross-sectional area between activeor functional electrode surfaces (surfaces of the electrodes from or towhich current contributing to electrochemical treatment of a fluid inthe electrochemical cell flows) through which fluid undergoing treatmentin the electrochemical cell may flow (an “active area” of theelectrochemical cell) to a total cross-sectional area within a housingof the electrochemical cell. “Active density,” as defined, is the areain a plane normal to the center axis through which fluid can flowdivided by the total cross-sectional area normal to the center axis. Theunit of measure is dimensionless, a fraction or a percentage. Aspectsand embodiments disclosed herein include electrochemical cells havingactive densities of between about 46% and about 52%, greater than about50%, in some embodiments, greater than about 75%, in some embodiments,greater than 85%, in some embodiments, greater than 90%, and in someembodiments up to about 95%.

As the term is used herein an “overall packing density” of anelectrochemical cell is defined as total functional electrode pathlength in a plane normal to flow of fluid through an electrochemicalcell respective to a total cross-sectional area within a housing of theelectrochemical cell. “Packing density” is the “active surface area” ofthe electrodes in an electrochemical device divided by the totalinternal volume of the device. The unit of measure is 1/length (e.g.m⁻¹). An “active surface area” of an electrode is the surface area ofthe electrode from which or into which current that contributes toelectrochemical reactions within an electrochemical device flows. Anelectrode having opposing surfaces may have active surface area on asingle surface or on both surfaces. An “anodic packing density” is the“active surface area” of the anode(s) in an electrochemical devicedivided by the total internal volume of the device. A “cathodic packingdensity” is the “active surface area” of the cathode(s) in anelectrochemical device divided by the total internal volume of thedevice. An “overall electrode packing density” or “total electrodepacking density” is the sum of the anodic packing density and cathodicpacking density of an electrochemical device. Aspects and embodiments ofelectrochemical cells disclosed herein may have anodic packingdensities, cathodic packing densities, and/or overall electrode packingdensities of 2 mm⁻¹ or more.

In accordance with certain embodiments, the anode and/or cathode tubesof an electrochemical cell may have apertures to allow hydrogengenerated in electrochemical reactions to flow through the electrodesmore easily and reduce hydrogen masking effects at the electrodesurface(s). Hydrogen masking reduces available anode area andsubsequently sodium hypochlorite output. Additionally or alternativelythe anode(s) and/or cathode(s) may include a fluid permeable and/orperforated or mesh material, for example, perforated titanium or atitanium mesh. The electrochemical cell may include a gas conduit foroxidant delivery to combine with hydrogen produced by, for example,electrochlorination reactions, in the cell and produce water or hydrogenperoxide. In some embodiments, a catalyst is provided, for example, onand/or in the cathodes to facilitate reaction of the oxidant andhydrogen in the cell.

The surface area of the electrodes may be increased through the use ofcorrugations. The electrochemical cell may include one of anodes orcathodes that are corrugated, while the other of the anodes or cathodesare non-corrugated. The electrochemical cell may include a multi-channelcorrugated electrode geometry. In other embodiments, the anodes andcathodes may have different forms of curvature than illustrated toprovide increased electrode surface area. However, it should be notedthat corrugations may increase turbulence, correspondingly decreasingaverage flow velocity through the electrochemical cell. Thus, corrugatedelectrode cells may require an increased inlet flow velocity tocompensate.

Surface area for hydrogen abatement at or in cathodes may be increasedthrough the use of multiple gas diffusion cathodes per anode. Themultiple gas diffusion cathodes may be supplied with gas (oxidant), forexample, oxygen, through axial or parallel gas conduits.

Aspects and embodiments of electrochemical cells disclosed herein mayinclude anodes and cathodes (or anode-cathode pairs) that are configuredand arranged to direct substantially all or all fluid passing throughactive areas or gaps between the anodes and cathodes in a directionsubstantially or completely parallel to a central axis of a housing. Insome embodiments, the gaps may be referred to as fluid channels. Thefluid channels may have a length of between 0.5 m and 2.0 m, forexample, about 1.0 m. In some embodiments, the fluid channels may extendat least 3.0 m. The direction substantially or completely parallelthrough the active areas may be parallel or substantially parallel tothe anodes and cathodes (or anode-cathode pairs). Fluid flowing throughthe active areas may still be considered flowing in the directionsubstantially or completely parallel through the active areas even ifthe fluid flow exhibits turbulence and/or vortices during flow throughthe active areas.

In some aspects and embodiments of electrochemical cells includingconcentric tube electrodes, for example, one or more anodes and/orcathodes as disclosed herein, the electrodes are configured and arrangedto direct fluid through one or more gaps between the electrodes in adirection parallel to a central axis of the electrochemical cell (shownas a dotted line in FIG. 3B). In some aspects and embodiments, theelectrodes are configured and arranged to direct all fluid introducedinto the electrochemical cell through the one or more gaps between theelectrodes in a direction parallel to a central axis of theelectrochemical cell. The width of the gaps between the electrodes maybe constant or variable. The width of the gaps between the electrodesmay be, for example, between about 1 mm and about 7 mm across, betweenabout 1 mm and about 5 mm across, or between about 3 mm and about 5 mmacross. In some embodiments, the width of the gap between electrodes maybe about 2.0 mm, about 2.5 mm, about 3.0 mm, about 3.5 mm, or about 4.0mm. The width of the gap and electrochemical cell design may be selectedbased on a type of electrolyte to be treated in the electrochemicalcell.

In an exemplary embodiment, a feed electrolyte solution flows throughthe two annular gaps (i.e. fluid channels) formed between the three tubeelectrodes. A DC voltage, constant or variable, or in some embodiments,an AC current, may be applied across the anode and cathode electricalconnectors. The current may flow from the inner and outer surfaces ofthe anode (middle tube electrode) simultaneously to the inner and outercathodes (inner tube electrode and outer tube electrode). Electricalconnection may be made between tube electrodes by one or more conductivebridges, which may be formed of the same material as the electrode, forexample, titanium. Electrochemical and chemical reactions may occur atthe surfaces of the electrodes and in the bulk solution to generate aproduct solution. For example, electrochemical and chemical reactionsmay occur at the surfaces of the electrodes and in the bulk solution togenerate a product solution in the fluid channels formed between thetube electrodes.

Electrochemical systems may generally be fed brine, brackish water, orseawater, although the feed solution is not limiting. Design parametersof the electrochemical cell may generally be selected based on thecomposition of the feed solution and/or desired composition of a productsolution. Seawater generally has a salinity of between about 3.0% and4.0%, for example, seawater may have a salinity of about 3.5%, 3.6%, or3.7%. Seawater comprises dissolved ions including sodium, chloride,magnesium, sulfate, and calcium. Seawater may further include one ormore of sulfur, potassium, bromide, carbon, and vanadium. Seawater mayhave a total dissolved solids (TDS) content of about 35,000 mg/l. Brinegenerally has a salinity of greater than about 3.5%. For example, brinemay have a salinity of about 4.0%, 4.5%, 5.0%, 7.5%, or about 10%. Brinemay have a TDS content of greater than about 35,000 mg/l. Saturatedbrine may have a salinity of up to about 25.0%. Brackish water generallyhas a salinity of less than 3.5%. Brackish water may have a salinity ofabout 3.0%, 2.5%, 2.0%, or 1.0%. Brackish water may have a TDS contentof less than about 35,000 mg/l. For example, brackish water may have aTDS content between about 1,000 mg/l to about 10,000 mg/l.

In general, the conductivity of the electrolyte solution may be betweenabout 0 and 25 S/cm, as dependent on the salinity. Brackish water havinga salinity between about 0.5% and 2.0% may have a conductivity ofbetween about 0.5 S/cm and about 4.0 S/cm, for example, about 0.8 S/cmor about 3.0 S/cm. Seawater having a salinity of about 3.5% may have aconductivity of between about 4.5 S/cm and 5.5 S/cm, for example, about5.0 S/cm or about 4.8 S/cm. Brine having a salinity between about 5.0%and 10% may have a conductivity of between about 7 S/cm and 13.0 S/cm,for example, about 12.6 S/cm. Saturated brine having a salinity of about25% may have a conductivity of between about 20.0 S/cm and about 23.0S/cm, for example, about 22.2 S/cm. Salinity and conductivity may followthe linear relationship: y=0.9132x+1.6332, where y is conductivity(S/cm) and x is percent salinity (% NaCl).

Scaling and fouling may generally occur in regions of low velocitywithin the electrochemical cell. Conventionally, acid washing may berequired to remove scaling. Acid washing requires the electrochemicalcell to be taken offline, limiting production and use. As disclosedherein, components of the electrochemical cell may be designed to reduceregions of low velocity, reducing scaling and fouling. The average fluidvelocity required to maintain self-cleaning properties may be dependenton the qualities of the electrolyte solution. As used herein, theself-cleaning fluid velocity is the average bulk fluid velocity by whichscale formation may be substantially minimized. The self-cleaning fluidvelocity may be selected to minimize, limit, or substantially reducescale formation in the electrochemical cell. Maintaining a self-cleaningfluid velocity and/or minimizing any zones of reduced velocity cansubstantially reduce or eliminate the need for acid washing of thedevice. Thus, the device can be maintained in continuous use for muchlonger periods of time, generally until an electrode or its coatingdegrades.

Typically, to maintain the self-cleaning nature of electrochemicalcells, for example, electrochemical cells employed to treat seawater,the bulk fluid velocity may be maintained above an average velocity of 2m/s. For example, seawater or water having a magnesium concentration ofabout 1000-1400 ppm and a calcium concentration of about 300-450 ppm atroom temperature (20-25° C.) may require an average flow velocity ofabout 2 m/s or greater to maintain self-cleaning properties. Seawater orwater having greater hardness, for example up to about 500 ppm Ca and1800 ppm Mg (water from the Red Sea) may require a greater average flowvelocity to maintain self-cleaning properties. Such seawater may requirean average flow velocity of about 2.5 m/s or 3.0 m/s to maintainself-cleaning properties. Seawater or water having less hardness, forexample, about 200 ppm Ca and about 700 ppm Mg (water from the ArabianGulf) may maintain self-cleaning properties with a lower average flowvelocity. For example, such seawater may maintain self-cleaningproperties at an average flow velocity of about 1.5 m/s or 1.8 m/s.

Seawater having a temperature greater than about 20° C. or 25° C. (forexample, water from the Arabian Gulf which may have a temperature ofabout 40° C.) or having a temperature less than about 20° C. or 25° C.(for example, water from the North Sea which may have a temperature ofabout 0° C.) may also maintain self-cleaning properties with a lower orgreater average flow velocity, respectively. Additionally, brackishwater and brine may maintain self-cleaning properties with lower averageflow velocities.

Average flow velocity may be maintained as required to maintainself-cleaning properties of the electrochemical cell. For instance, flowvelocity may be maintained at greater than about 1.5 m/s, between about1.5 m/s and about 2 m/s, greater than about 2 m/s, between about 2 m/sand about 2.5 m/s, greater than about 2.5 m/s, between about 2.5 m/s and3.0 m/s, or greater than about 3.5 m/s as required to maintainself-cleaning properties with the particular electrolyte solution. Forcertain feed streams, flow velocity may be maintained at or near 4 m/s,5 m/s, 6 m/s, 7 m/s, 8 m/s, 9 m/s, or 10 m/s. Any average velocity belowthe self-cleaning velocity may be resolved within a predeterminedlength, as described in more detail below.

In some embodiments disclosed herein, the electrodes, e.g., a cathodeand an anode, may be disposed concentrically in a housing about acentral axis of the housing. The electrodes can be inserted into anon-metallic housing and connected to a source of DC or AC power bywaterproof connectors so that no electrically live components areexposed to the outside environment. This design is generally safer forthe operators and there is no risk of short-circuit between the devicesand an external grounded component or liquid.

The electrodes may be positioned inside a non-metallic housing, designedto electrically isolate the electrodes from the outside environment andto withstand the fluid pressure of electrolyte passing through theelectrochemical cell. The housing may be non-conductive, chemicallynon-reactive to electrolyte solutions, and have sufficient strength towithstand system pressures, system high-frequency vibrations, andenvironmental low-frequency vibrations (for example, onboard a ship).The housing may have sufficient strength to withstand up to 16 Barpressure. The housing may have sufficient strength to withstand anelectrolyte solution flow rate of up to 10 m/s. The housing may compriseone or more of polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVDF), acrylonitrile butadiene styrene (ABS),high-density polyethylene (HDPE), fiber reinforced polymer (FRP), orother appropriate materials, and in some embodiments may includereinforcing elements, for example, glass or carbon fibers embedded in apolymer matrix. Electrode connectors may extend outside the walls of thehousing at an end of the housing. In some embodiments, the electrodeconnectors may extend outside the walls of the housing at opposite endsof the housing.

As shown in FIGS. 3A-3C, the electrochemical cell 1000 may contain oneor more separators 1180 configured to maintain the gap betweenelectrodes 1020 and 1040. The separators 1180 may be positioned toreside between the electrodes 1020 and 1040 (as shown in FIG. 3C), e.g.,between a cathode and an anode. To maintain the fluid channel (shown inFIG. 3C between electrodes 1020 and 1040), the separators 1180 may bedimensioned to have a height which maintains the width of the gapbetween the electrodes 1020 and 1040, localizing the electrodes 1020 and1040 and maintaining concentricity of the tubes (as shown in FIG. 3B).The separators 1180 may be dimensioned to allow fluid flow through thechannel.

FIGS. 7A-7B show another embodiment of separators 1180. As shown in FIG.7A, each separator 1180 may be constructed and arranged to attach to theend of an electrode tube 1020, 1040. The separators may be positionedwithin electrode tubes 1020, 1040 as shown in FIG. 7B. The separator1180 may contain one or more features 1186 that mate with an electrodeor electrical connector. As used herein, “mate” refers to a connectionbetween two or more elements. The connection may be mechanical and/orelectrical. The mating feature may be used to maintain alignment andprevent rotation of the separator relative to the electrode orelectrical connector. The molded features 1186, as shown in FIGS. 7C-7Dmay facilitate assembly of the electrochemical cell by reducing the needfor other attachment elements. In some embodiments, the separator maycomprise a slot, clamp, or integral attachment feature configured tomate with an electrode tube and maintain concentricity of concentricelectrode tubes.

The separator may be constructed from a chemically-inert, non-conductivematerial capable of withstanding high pressure. In some embodiments, theseparator may be constructed to withstand up to 16 Bar pressure, systemhigh-frequency vibrations, and environmental low-frequency vibrations(for example, onboard a ship). The separator may be constructed towithstand an electrolyte solution flow rate of up to 10 m/s. Theseparator may be constructed from plastic or ceramic. The separator maycomprise one or more of PVC, PTFE, PVDF, ABS, HDPE, FRP, or otherappropriate materials. In some embodiments, the separator may beinjection molded for ease of manufacturing and assembly.

Flow features such as separators tend to create drag on the flowingelectrolyte solution, resulting in an area of reduced velocity (alsodescribed herein as a “zone of reduced velocity”) downstream from theseparator. As previously described, a decrease in average flow velocitymay compromise the self-cleaning nature of an electrochemical cell.Thus, any average velocity below the self-cleaning velocity should beresolved within a predetermined length down the fluid channel from theseparator. A self-cleaning electrochemical cell with no separator mayresolve a zone of reduced velocity, for example, within 20 mm from theinlet of the electrochemical cell. In some exemplary embodiments,self-cleaning properties are met when the zone of reduced velocity isresolved within 140 mm from the separator, as shown in FIG. 4 .According to some embodiments, the separator may be dimensioned toresolve the zone of reduced velocity within 20 mm (FIG. 4 ) or within 60mm (FIG. 5 ).

The zone of reduced velocity may be defined by an area in which theelectrolyte solution flow velocity is lower than the average flowvelocity of the solution through the channel or the self-cleaningvelocity. The zone of reduced velocity resulting from the separator isgenerally located downstream of the separator, but other zones ofreduced velocity may exist within the electrochemical cell. In someembodiments, the zone of reduced velocity is defined by an area in whichan average electrolyte solution flow velocity is at least 2%, 5%, 10%,15%, 20%, or 25% less than the self-cleaning velocity or the averagevelocity through the fluid channel. For an exemplary electrochemicalcell having a self-cleaning or average flow velocity of at least 2 m/s,the zone of reduced velocity may be defined by any flow velocity lowerthan 2 m/s, by a flow velocity at least 25% lower than 2 m/s (forexample, 1.5 m/s), by a flow velocity at least 20% lower than 2 m/s (forexample, 1.6 m/s), by a flow velocity at least 15% lower than 2 m/s (forexample, 1.7 m/s), by a flow velocity at least 10% lower than 2 m/s (forexample, 1.8 m/s), by a flow velocity at least 5% lower than 2 m/s (forexample, 1.9 m/s), by a flow velocity at least 2% lower than 2 m/s (forexample, 1.96 m/s), or by a flow velocity at least any other percentagelower than 2 m/s.

For any average flow velocity within the zone of reduced velocity, thezone may end when the fluid velocity resolves to an average bulkvelocity equal to the self-cleaning fluid velocity or equal to theaverage fluid velocity within the electrochemical cell. For example, thezone of reduced velocity may have a given velocity profile whichresolves when the average fluid velocity reaches 2 m/s (or any otherdesired self-cleaning velocity). In some embodiments, the zone ofreduced velocity ends when the average fluid velocity reaches a velocitywithin 1%, 2%, 5%, or 10% of the self-cleaning velocity or the averagevelocity within the electrochemical cell. Thus, for an exemplaryelectrochemical cell having a self-cleaning velocity of 2 m/s, the zoneof reduced velocity may end when the average fluid velocity resolves to2 m/s, 1.98 m/s (within 1%), 1.96 m/s (within 2%), 1.9 m/s (within 5%),or 1.8 m/s (within 10%). In some embodiments, the zone of reducedvelocity ends when the average fluid velocity resolves to the inletfluid velocity, for example, the fluid velocity upstream from theseparator. The zone of reduced velocity may end when the average fluidvelocity resolves to a fluid velocity within 1%, 2%, 5%, or 10% of theinlet fluid velocity.

The zone of reduced velocity may also be characterized by a velocitydeviation from the mean flow velocity of the bulk electrolyte solutionthrough the electrochemical cell. The velocity spread within the zone ofreduced velocity is generally greatest at the boundary of the zone ofreduced velocity and the separator (i.e., immediately downstream fromthe separator). The velocity spread tends to normalize downstream, untilit is within a percentage from the mean flow velocity of theelectrochemical cell. In an exemplary embodiment, the velocity spreadfollows the curve of the graph of FIG. 22 . In some embodiments, thevelocity deviation within the zone of reduced velocity does not exceed±20%, for example, does not exceed ±18%, does not exceed ±15%, of themean flow velocity. The zone of reduced velocity may terminate when thevelocity spread is within ±5%, within ±2%, within ±1% of the mean flowvelocity. Since the mean flow velocity is, by definition, an averagevelocity, it is conceivable that the velocity spread may remain within asmall percentage from the self-cleaning velocity throughout the lengthof the electrochemical cell.

The separator may be designed to minimize the zone of reduced velocitywhich naturally occurs in the fluid channel downstream of the separator.The zone of reduced velocity is minimized to maintain the self-cleaningproperties of the electrochemical cell. The separator may be dimensionedto maintain the zone of reduced velocity within a predetermined length.Generally, the predetermined length of the zone of reduced velocity maybe selected to minimize or eliminate scaling based on the average flowvelocity through the fluid channel and/or the composition of theelectrolyte solution. The predetermined length can be, for example,between about 2% and 5%, for example, less than about 5% of a length ofthe fluid channel. In some embodiments, the predetermined length isabout 5%, 4%, 3%, 2%, or less than 1% of the fluid channel. Certainelectrolyte solutions may tolerate a greater predetermined length thanothers. Composition, hardness, and temperature of the electrolytesolution may play a role in determining the tolerance of theelectrochemical cell for scaling.

In some embodiments, the predetermined length is described in relationto a width of the flow channel. For instance, the ratio of the length ofthe zone of reduced velocity to the width of the fluid channel may beless than 120 to 3.5. This ratio corresponds to a zone of reducedvelocity having a length of less than 120 mm for a channel width of 3.5mm, a length of less than 102.8 mm for a channel width of 3.0 mm, alength of less than 85.7 mm for a channel width of 2.5 mm, and so forth.The ratio of the length of the zone of reduced velocity to the width ofthe fluid channel may be less than 100 to 3.5, 60 to 3.5, or 20 to 3.5.In some embodiments, the predetermined length may be within 140 mm, 120mm, 100 mm, 60 mm, or 20 mm for an electrolyte solution flowing throughthe fluid channel at an average flow velocity of between 2.0 m/s and 2.5m/s, for example, 2.0 m/s, 2.1 m/s, 2.2 m/s, 2.3 m/s, 2.4 m/s, or 2.5m/s.

In some embodiments, the separator is designed to minimize the zone ofreduced velocity by allowing only a predetermined flow area through thechannel. The separator may be dimensioned to have a cross-sectional areathat covers a predetermined percentage of a flow area of the fluidchannel. For instance, the separator may be dimensioned to have across-sectional area between 10% and 35% of the flow area of the fluidchannel. The separator may be dimensioned to have a cross-sectional arealess than about 10%, 15%, 20%, 25%, 30%, or 35% of the flow area of thefluid channel. In general, the separator may be designed to have across-sectional area that is as small as possible (i.e., allowing thegreatest solution flow) while supporting the fluid channel. Thecross-sectional area of the separator may be designed to provideadequate support to the electrode tubes to maintain concentricity, whilereducing the zone of reduced velocity that occurs downstream from theseparator to maintain the self-cleaning properties of theelectrochemical cell.

The separator may be designed to maintain an electrolyte solutionvelocity deviation from mean to be within ±20%, for example, ±18%, or±15%, of an average flow velocity of the electrolyte solution throughthe fluid channel. The separator may be dimensioned to minimize thevelocity deviation from mean downstream from the separator. For example,the separator may minimize the velocity deviation from mean immediatelyadjacent to the separator. In some embodiments, the separator may beaqualined to minimize the velocity deviation from mean. As describedherein, “aqualined” may refer to a component having a streamlinedconfiguration against a flow of solution. Aqualined may compriseconfigurations which form minimal downstream velocity deviations frommean. In some embodiments, aqualined configurations do not orsubstantially do not form eddies downstream. Aqualined configurationsneed not be limited to providing laminar flow and may be surrounded byturbulent flow. In some embodiments, aqualined configurations do notsubstantially contribute to turbulence in the flow of electrolytethrough the electrochemical cell.

In accordance with certain embodiments, as shown in FIG. 6A, theseparator may comprise a ring 1182 and a plurality of projections 1184extending from the ring 1182. The separator may allow fluid flow betweenthe projections 1182 (for example, as shown in FIG. 3C). The feature1186 provided for alignment of the separator may be positioned on thering 1182, for example, between adjacent projections. The projections1184 may be provided to maintain the gap between the electrode tubes,while allowing fluid flow through the channel. Thus, the projections maybe dimensioned to have a height which maintains the width of the fluidchannel. As shown in FIGS. 6B-6D, H is the height of the projectionessentially equivalent to the width of the fluid channel, W is a widthof the projection, and L is a length of the projection down the fluidchannel. The projections 1184 may be attached to the ring 1182 on oneend and extend radially outward from the ring or radially inward fromthe ring. In embodiments where projections extend radially outward andradially inward from the ring, as shown in FIG. 6A, the height may beessentially equivalent to half the width of the fluid channel.

Typically, the projections may have a length L (defined in a directiondown the flow channel), as shown in FIGS. 6C and 6D, that is greaterthan the width W. Additionally, the projections may have a streamlinedor aqualined configuration to reduce drag on the flowing electrolyte. Insome embodiments, the projections may be spherical, cylindrical, ovoid,teardrop shaped, almond shaped, diamond shaped (elongated orsymmetrical), or a rounded triangle. The projections may have acircular, oval, triangular, diamond, or teardrop cross-sectional shape.

The separator may generally have sufficient projections to providesupport for the electrode tubes. In some embodiments, the separator mayhave between 2 and 8 projections, for example, between 3 and 6projections. The separators may have, for example, 3, 4, 5, or 6projections. The dimensions of the ring and projections may be designedto reduce the zone of reduced velocity. For instance, the number andarrangement of projections may be selected to minimize the zone ofreduce velocity or otherwise maintain the zone of reduced velocitywithin the predetermined length. Accordingly, the separator may have anumber and width of projections that result in a separatorcross-sectional area between 10% and 35% of the flow area of the fluidchannel. In some embodiments, the projections may be substantiallyevenly spaced apart on the ring to provide even support (for example, asshown in FIG. 6A). Similarly, the length and width of projections may beselected to minimize the zone of reduced velocity or otherwise maintainthe zone of reduced velocity within the predetermined length. Theprojections may be dimensioned to have a width that provides sufficientstructural support for the electrodes (for example, based on the numberof projections) while not substantially exceeding a width that wouldprovide too much drag. For certain materials, the projections may have aminimum width capable of manufacture that also provides adequatesupport. In some embodiments, the projections may be dimensioned to havea width that is between 0.5 and 2 times the height, for example, between0.5 and 1 times the height or between 1 and 2 times the height.

A typical electrochlorination cell may have a channel width of between 1and 5 mm. Such an electrochemical cell may contain a separator having aring width of between 0.5 and 3 mm, projections having a height ofbetween 1 and 5 mm (correlating with the channel width), projectionshaving a width of between 1 and 10 mm, and projections having a lengthof between 1 and 10 mm. An exemplary electrochemical cell may have achannel width of 3.0 to 3.5 mm. Such an electrochemical cell may includea ring having a width of 1 mm and projections having a width of 2.5 to 7mm and a length of 5 to 10 mm, where the length is not shorter than thewidth. The ring may be substantially centrally located in the fluidchannel, with projections extending in both directions from the ring.The height of projections in this exemplary ring may be measured fromend to end. In some embodiments, the ring may be positioned against oneof the electrodes, with projections extending in substantially onedirection toward the opposite electrode.

As previously described, the electrochemical cell can include aplurality of concentric tube electrodes, for example, three, four, orfive concentric tube electrodes. With each added concentric tubeelectrode, an additional cathode electrode surface, an additional anodeelectrode surface, and an additional fluid channel are provided. Eachfluid channel may be defined between each adjacent cathode and anode,and each fluid channel may extend substantially parallel to the otherfluid channels and a central axis of the housing. Each fluid channel mayadditionally be associated with a separator residing between theelectrodes to maintain the fluid channel. Thus, the electrochemical cellmay comprise a plurality of concentric separators residing betweenconcentric electrodes.

In some embodiments, for example, as shown in FIG. 16 , theelectrochemical cell 1000 may comprise a plurality of consecutiveelectrodes 1020, 1022. The consecutive electrodes 1020, 1022 may bearranged down a length of the housing (not shown in FIG. 16 ). As shownin FIGS. 17A-17C, the electrochemical cell 1000 may include one or moreseparators 1200 positioned between consecutive electrodes 1020, 1022.The separators 1200 may be positioned, arranged and configured to matewith the consecutive electrodes 1020, 1022 (for example, through afeature such as a slot, clamp, or electrical connection), locating theelectrodes within the electrochemical cell 1000. Additionally, whereconcentric 1020, 1040 and consecutive 1020, 1022 electrodes are present,a plurality of concentric separators 1200 may be positioned betweenconsecutive electrodes 1020, 1022 and configured to maintainconcentricity of the consecutive electrodes, for example, as shown inFIGS. 18A and 18B.

The separators positioned between consecutive electrodes may comprise aplurality of contiguous rings 1220. Several embodiments of contiguousrings 1220 are shown in FIGS. 19-21 . For example, the separator maycomprise two, three, or four contiguous rings. In some embodiments, atleast one of the contiguous rings comprises a plurality of projections,as previously described. The contiguous rings may be configured to matewith each other and/or with an adjacent consecutive electrode. Any gapsoccurring between the contiguous rings may be minimized to reduce a zoneof reduced velocity existing downstream from the separator. Forinstance, the gap between contiguous rings may be dimensioned tomaintain the zone of reduced velocity within a predetermined length, aspreviously described. In some embodiments, seals may be implementedbetween contiguous rings to reduce the effective gap, and thus the zoneof reduced velocity.

The gap between contiguous rings may be less than 1.60 times a width ofthe separator, for example, of a ring of the separator. For example, theseparator may comprise a ring having a width between 1 and 3 mm. Thegaps between contiguous rings may be less than 4.80 mm, less than 3.20mm, or less than 1.60 mm. The width of the gap may be between 0.5 and4.80 mm, between 0.5 and 3.20 mm, or between 0.5 and 1.60 mm. In anexemplary embodiment, the separator may comprise a plurality ofcontiguous rings having a width of 1 mm, wherein gaps between the eachtwo of the plurality of rings have a width between 0.5 and 1.60 mm. Ingeneral, the width of the gap between contiguous rings may bedimensioned to be as small physically possible. If possible formanufacture, the contiguous rings may have substantially no gap betweenthem.

In accordance with certain embodiments, for example, as shown in FIGS.8A and 8B, the electrochemical cell 1000 may include inlet and outletend caps 1060 and 1080, each coupled to a distal end of the housing1160. The end caps 1060, 1080 may have a substantially centrally locatedaperture 1062 (as shown in FIGS. 9A and 9B, which are top and bottomviews of an end cap, respectively). As shown in the cross-sectional viewof FIG. 8B, the apertures may be in fluid communication with fluidchannels between anodes and cathodes in the interior of theelectrochemical cell. The end caps may further include fluid conduits1064 (as shown in the cross-sectional view of FIG. 9D) providing fluidcommunication between the apertures and the fluid channel of theelectrochemical cell. Fluid, for example, electrolyte solution, may thusbe introduced into the electrochemical cell through one or more fluidconduit of the inlet end cap and continue through the gap between theelectrodes, i.e., the fluid channel. The fluid may exit theelectrochemical cell through a fluid conduit of the outlet end cap andout the substantially centrally located aperture.

The fluid conduit within the end cap may be designed to minimize apressure drop across the electrochemical cell. In a cylindrical pipe,the pressure loss due to viscous effects is proportional to length andcharacterized by the Darcy-Weisbach equation:

$\frac{\Delta\; p}{L} = {f_{D} \cdot \frac{\rho}{2} \cdot \frac{\left\langle v \right\rangle^{2}}{D}}$

where:

Δp is pressure loss (Pa),

L is length of the conduit (m),

D is hydraulic diameter (m),

f_(D) is friction factor (determined by Reynolds number, absoluteroughness and relative roughness of the material, and coefficient offriction),

ρ is density of the fluid (kg/m³), and

ν

is the mean flow velocity (m/s).

Thus, pressure drop may vary with length, hydraulic diameter, andmaterial of the conduit. In some embodiments, a radius and/or length ofthe fluid conduit may be dimensioned to minimize pressure drop withinthe electrochemical cell. Additionally, fluid density and flow velocitymay also have an effect on pressure drop.

The pressure drop may be determined by the difference between inletpressure and outlet pressure through an electrochemical cell. In someembodiments, minimizing pressure drop includes minimizing inletpressure. Thus, in some embodiments, a radius and/or length of the fluidconduit of an inlet end cap may be dimensioned to maintain a desiredinlet pressure. Inlet pressure may be maintained below, for example, 125kPa, 122 kPa, 120 kPa, 118 kPa, 117 kPa, 116 kPa, or 115 kPa. However,inlet pressure should be maintained within a range that promotessuitable use of the electrochemical cell. Inlet pressure may bemaintained between about 115 kPa and 125 kPa, for example, between about117 kPa and 121 kPa. Outlet pressure may be maintained between about 100kPa and 105 kPa, for example, between about 101 kPa and 103 kPa. Aminimized pressure drop may be as close to substantially no pressuredrop as allowable by manufacturing and material constraints, forexample, below 25 kPa, 24 kPa, 23 kPa, 22 kPa, 21 kPa, 20 kPa, below 19kPa, below 18 kPa, below 17 kPa, below 16 kPa, below 15 kPa, or lower.The minimized pressure drop may be dependent on the electrolyte solutionfluid density and average flow velocity (for example, self-cleaning flowvelocity for such a fluid).

In some embodiments, the fluid conduit includes a zone of a first radiusand a zone of a second radius greater than the first radius. The zone ofthe first radius may be adjacent to the substantially centrally locatedaperture, while the zone of the second radius may be adjacent the fluidchannel. In an exemplary embodiment, the fluid conduit of the inlet endcap has a first linear region, a radially increasing region, and asecond linear region, where the first linear region may correspond tothe first radius and the second linear region may correspond to thesecond radius. The end cap may comprise a feature for mating with theend of the housing.

The end caps may be constructed from a chemically-inert, non-conductivematerial capable of withstanding high pressure. In some embodiments, theend caps may be constructed to withstand up to 16 Bar pressure, systemhigh-frequency vibrations, and environmental low-frequency vibrations(for example, onboard a ship). The end caps may be constructed towithstand an electrolyte solution flow rate of up to 10 m/s. The endcaps may be constructed from plastic or ceramic. The end caps maycomprise one or more of PVC, PTFE, PVDF, ABS, HDPE, FRP, or otherappropriate materials.

As shown in FIGS. 10A and 10B, the electrochemical cell may furthercomprise a cone 1120 disposed within the fluid conduit of the end cap1060 and configured to define a flow path for a solution into the fluidchannel. The cone 1120 may be coupled to the housing 1160 to define aflow path into the fluid channel. In some embodiments, the cone may becoupled to the electrode 1020 (as shown in FIG. 11A), electricalconnector 1240 (as shown in FIG. 11B), or other element of theelectrochemical cell, to define a fluid flow path into the fluidchannel. Thus, the cone may have a base diameter equal or substantiallyequal to an inner diameter of the fluid channel.

As previously described, pressure drop across an electrochemical cellmay vary with hydraulic diameter. The inlet cone 1120, outlet cone 1140,or both (as shown in FIG. 8B) may be designed to minimize the pressuredrop across the electrochemical cell, for example, by altering ahydraulic diameter of the flow path. FIG. 12 is a contour map ofpressure drop across an exemplary electrochemical cell. As shown in FIG.12 , there is a pressure differential across the fluid channel. Varyingthe dimensions of the inlet end cap fluid channel may have an effect oninlet pressure, as shown in FIGS. 13A-C. Additionally, varying thedimensions of the inlet cone may have an effect on pressure drop, asshown in FIG. 14A and the data presented in the graph of FIG. 14B.

Minimizing the pressure drop may include, for example, maintaining asubstantially constant flow area between the fluid conduit and the cone.Generally, the cone may have a base that is dimensioned to correspondwith the fluid channel. For an annular fluid channel, the base may havea diameter that substantially corresponds with an inner diameter of theannular fluid channel. In addition to designing the dimensions of thefluid conduit to reduce pressure drop, one or more of height, apexangle, base angle, and slant height of the cone may be dimensioned tominimize the pressure drop across the electrochemical cell. The inletcone, outlet cone, or both may independently have an apex angle ofbetween 20° and 90°, for example between 30° and 80° or between 40° and60°. The inlet cone, outlet cone, or both may independently have an apexangle of 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90° or as necessary tominimize pressure drop across the electrochemical cell.

In some embodiments, for example, as shown in FIGS. 15A and 15B, theelectrochemical cell includes an outlet frustrum 1122 in lieu of anoutlet cone. The outlet frustrum 1122 may be disposed within the fluidconduit 1064 of the outlet end cap 1080 and configured to define a flowpath for a solution out of the electrochemical cell. The outlet frustrum1122 may be dimensioned to further minimize pressure drop across theelectrochemical cell, as shown in the contour maps. By modifying theoutlet cone to produce an outlet frustrum, total flow area of the outletend cap is increased resulting in a further reduced pressure drop.

The fluid conduit of the end cap may be dimensioned to allowfully-developed flow of the solution. Additionally, the flow pathdefined between the fluid conduit and the cone can be dimensioned tomaintain the fully-developed flow of the solution. As used herein,fully-developed flow occurs when the boundary layer of the flow throughthe fluid conduit expands to fill the entire conduit, such that the flowcharacteristics remain substantially the same throughout the remaininglength of the conduit. The entrance length is the conduit lengthrequired so that the fluid flow becomes fully-developed. The length ofthe flow path may be greater than the entrance length of the particularsolution, such that the flow traveling between the conduit and the conebecomes and/or remains fully-developed.

The flow path may have a hydraulic diameter defined by the space betweenthe cone and the fluid conduit. In some embodiments, the flow path mayhave a hydraulic diameter that is between 2 and 10 times the length ofthe greater linear region of the fluid conduit (i.e. the zone of thesecond radius) to maintain fully-developed flow. The flow path may havea hydraulic diameter that is at least 2, 3, 4, 5, 6, 7, 8, 9, or 10times the length of the zone of the second radius, or as necessary tomaintain fully-developed flow of the particular electrolyte solution. Ingeneral, the length of the zone of the second radius may be as large aspossible, while maintaining an adequate inlet pressure and pressure dropacross the electrochemical cell.

The end caps could potentially serve dual purposes, as they could alsoincorporate electrical connectors for the delivery of current toelectrodes and provide a pneumatic seal for the electrochemical cell.For instance, end caps when fastened to opposing ends of theelectrochemical cell, may form pneumatically sealed chambers. The capsmay provide a configuration for pneumatic and electrical routing of thegas conduits.

As shown in FIGS. 23A-23D, the electrochemical cell 1000 may includeelectrical connectors 1240 positioned at distal ends of the electrodesand electrically connected to the electrodes. Electrical current may beapplied to the electrochemical cell through an electrical connector,travel internally through the electrodes and process fluids, and exitthe electrochemical cell through a corresponding ground connection. Themaximum current applied to an electrochemical cell may be defined by itsoperational current density, generally less than about 3000 A/m². Theoperational current density may vary with electrode coating and internalelectrode surface area. During design of the electrochemical cell,resistance may vary with surface area of the electrical connector,applied current, resistivity of the cell material, and heat capacityrate of the cell.

The electrical connectors may be made of any conductive, corrosionresistant material. In some embodiments, the electrical connectors maybe made of the same material as one or more of the electrodes, forexample, titanium. The electrical connector may be fixed to theelectrodes, for example, via a mating feature or welding. The electricalconnector may be manufactured from a continuous conductive sheet or maycontain features that are welded or otherwise conductively joinedtogether. Conventionally, electrical connectors are easy to manufacturebut are not designed to be aqualined. Thus, the conventional electricalconnectors generally create a large region of low flow velocitydownstream.

A first electrical connector may be provided on a first end of amulti-tube electrochemical cell as disclosed herein to provideelectrical contact to the anode electrode tube(s) and a secondelectrical connector may be provided on a second end of a multi-tubeelectrochemical cell as disclosed herein to provide electrical contactto the cathode electrode tube(s). Apertures may be provided in theelectrical connectors to allow fluid to flow through the gaps betweenthe concentric electrode tubes. Spokes of the electrical connectors mayhave positioning elements, for example, slots, tabs, pins, and/orprotrusions at intervals, for example, to engage the electrode tubesand/or spacers. An outer rim of the electrical connector can beconnected to a source of power utilizing a single connector or multipleconnectors.

The connection between an electrical connector and an electrical wirefrom a power source can be sealed and isolated from the environment, forexample with gaskets, screws, and/or bolts, for safety and corrosionprevention. Waterproof connectors (for example, IP54 connectors) may beused to connect the electrical connector to the source of power. Certainembodiments may also provide for a high ingress protection (IP) rating,which protects operators from shock hazard and dispenses with the needfor an expensive weatherproof enclosure. In an exemplary embodiment,high density plastic pipework components using, for example, ABS, U-PVC,C-PVC, and/or PVDF material may be used to seal and isolate theelectrical connector due to their chemical resistance, for example, tosodium hypochlorite and a high achievable pressure rating in the rangeof about 5 to about 15 Bar. Commercially available high IP rated cableconnectors may be used to transfer current to and from the electrodes.

The electrical connectors may be designed to minimize electricalresistance and heat generation. Generally, the electrical resistance isa function of device geometry and material resistivity. Heat generationincreases with increasing resistance in accordance with the Joule-Lenzlaw, which provides that the power of heat generated by an electricalconductor is proportional to the product of its resistance and thesquare of the current. When operated in series, heat generated withineach electrochemical cell is cumulative across the series and should beminimized. However, applied current should be maintained within anappropriate range to generate the desired product. Thus, in someembodiments, the electrical connectors may be dimensioned to minimizeresistance (and therefore, heat generation) for a given material whileproviding adequate current.

In an exemplary embodiment, the electrical connector may be titaniumbased. The electrical connectors may be operated to transmit between 25W and 1.5 kW of power to the electrodes, for example between 25 W and100 W, between 100 W and 1 kW, or between 1 kW and 1.5 kW. Theelectrical connectors may be dimensioned to generate less than about 100W of heat, for example, less than about 75 W of heat, less than about 50W of heat, or less than about 25 W of heat. In some embodiments, theelectrical connectors may be dimensioned to generate less than about 25W of heat when transmitting at least 100 W of power to the at least oneof the plurality of electrodes. In such an embodiment, the electricalconnector may be dimensioned to generate less than 1° C., for example,less than about 0.5° C. or less than about 0.1° C. when transmitting atleast 100 W of power. FIG. 25C is a contour map of heat generated at theelectrical connector. As shown in the exemplary embodiment of FIG. 25C,temperature of the fluid increases from about 20.05° C. at the inlet toup to 20.10° C. following the electrical connector and around 20.07° C.at the outlet of the electrochemical cell. In other embodiments, theelectrical connectors may be dimensioned to generate less than about 25W of heat when transmitting at least 1 kW of power, dimensioned togenerate less than about 100 W of heat when transmitting at least 1 kWof power, or dimensioned to generate less than about 100 W of heat whentransmitting at least 1.5 kW of power. The power transmitted may dependon the operational requirements.

The electrical connector may be designed to minimize a zone of reducedvelocity which occurs downstream from the electrical connector. FIG. 25Dis a contour map of velocity downstream from an exemplary electricalconnector. As previously mentioned with respect to the separators, thezone of reduced velocity is minimized to maintain the self-cleaningproperties of the electrochemical cell. The electrochemical connectionmay be dimensioned to maintain the zone of reduced velocity within thepredetermined length, as previously described.

The electrical connectors may additionally be designed to provide asubstantially uniform current distribution around the concentricelectrodes. Current distribution around an inner electrode 1020 and anouter electrode 1040 are shown in FIG. 25B. The electrical connectorsmay have a symmetric or substantially symmetric geometry to providesubstantially uniform current distribution.

As shown in FIGS. 24A-24C, the electrical connector 1240 may include awheel 1242 and spokes 1244. Each wheel 1242 may be configured to provideelectrical connection to a corresponding electrode tube. Thus, forembodiments with multiple concentric electrode tubes, the electricalconnector may include corresponding concentric wheels. The spokes may beconfigured to provide electrical connection between concentric wheels.In some embodiments, the spokes may be rectilinear for ease ofmanufacturing and to reduce resistance, but may be of any geometrydesired. The electrical resistance of a spoke can be defined by thebelow equation:R=ρH/(W×L)

where:

R is resistance,

ρ is material resistivity,

H is spoke height, determined by the gap between concentric wheels,

W is spoke width around the circumference of the wheel, and

L is spoke length down the fluid channel.

The number and dimensions of spokes may be selected to minimizeresistance, heat generation, and the zone of reduced velocity created bythe electrical connector. The resistance of an individual spoke shouldresult in an ohmic loss of less than about 50 W, for example, less thanabout 25 W or less than about 10 W. The maximum tolerated ohmic loss ofa spoke and electrical connector may be selected based on the desiredelectrochemical reaction in conjunction with the heat capacity rate ofthe particular electrolyte solution flowing through the electrochemicalcell.

In general, the height of the spoke, identified by H in FIG. 24B, may bedetermined by the gap between concentric wheels. Thus, the height maysubstantially correspond to the width of a fluid channel. In someembodiments, where alternating electrodes are electrically connected,the height may substantially correspond to the width of two or moreconcentric fluid channels. The height may be between about 1 and 20 mm,for example about 20 mm, about 16 mm, about 14 mm, about 10 mm, about 8mm, about 7 mm, about 6 mm, about 5 mm, about 3.5 mm, about 3 mm, orsubstantially equivalent to the width of one or more fluid channels. Inembodiments where the wheel of the electrical connector has a smallerwidth than the electrode, the height of the spoke may be greater thanthe width of one or more fluid channels, as necessary to provideconnection between concentric adjacent or non-adjacent wheels.

The width of the spoke, identified by W in FIG. 24B, may be dimensionedto minimize the length of the zone of reduced velocity (as describedabove with respect to the separator) while providing adequate electricalconnection between concentric wheels. In some embodiments, the width ofthe spoke may be between 0.25 and 2 times the height of the spoke. Forexample, the width of the spoke may be between about 0.5 mm and about 10mm, between about 0.5 mm and about 7 mm, between about 0.5 mm and about5 mm, between about 0.5 mm and about 3 mm, between about 0.5 mm andabout 2 mm, or between about 0.5 mm and about 1 mm. The width of thespoke may be between about 1 mm and about 20 mm, between about 1 mm andabout 15 mm, between about 1 mm and about 12 mm, or between about 1 mmand about 10 mm. The width of the spoke may be as small as necessary toreduce drag of the fluid, but adequate for providing electricalconnection between concentric wheels. In some embodiments, the materialmay be selected to provide adequate resistance in a small volume.Conventionally, manufacturing constraints have restricted the selectionof size of the electrical connector. However, titanium can providegreater resistivity in a small volume, reducing the zone of reducedvelocity. Furthermore, the spokes and/or wheels can be aqualined tofurther reduce the zone of reduced velocity.

The length of the spoke, identified by L in FIG. 24C, may be dimensionedto minimize electrical resistance and heat generation, while maintaininga desired power dissipation. For a given height (the gap betweenconcentric wheels) and width (the width selected to minimize the zone ofreduced velocity), the length can be selected based on a thresholdresistance using the equation above. Furthermore, the resistance may beselected to minimize heat generation, as described above. In someembodiments, the length may be between about 1 mm and about 15 mm, forexample, between about 5 mm and 15 mm or between about 7.5 mm and 15 mm.

The resistance, heat generation, power dissipation, and zone of reducedvelocity of the electrical connector may also be dependent on the numberof spokes provided. In some embodiments, the number of spokes isselected to minimize electrical resistance, minimize heat generation,minimize zone of reduced velocity, or provide adequate powerdissipation. The electrical connectors may include between about 1 and 8spokes between adjacent wheels, for example, between about 2 and 6spokes or between about 3 and 6 spokes, or as necessary to meet thedesired requirements.

In general, the amount of current through a spoke may be determined bythe applied current, surface area of the tubular electrode, and numberand distribution of spokes. The arrangement of spokes on the electricalconnector may have an effect on current distribution across thewheel(s). In some embodiments, the spokes may be substantially evenlydistributed to provide uniform current distribution. In an exemplaryembodiment, current distribution improves with an increasing number ofspokes, wherein the spokes are substantially evenly distributed acrossthe wheel. Thus, the number and arrangement of spokes may be selected toprovide adequate current distribution, while maintaining the zone ofreduced velocity within a predetermined length to maintain self-cleaningproperties of the electrochemical cell, as described above.

Furthermore, the arrangement of spokes on a first wheel with respect tospokes on an adjacent concentric wheel may have an effect on currentdistribution. Spokes on adjacent wheels may be arranged collinearly(i.e. aligned with each other) or may be angularly offset from eachother. In some embodiments, spokes provided on adjacent concentricwheels may be substantially evenly offset from each other to provideuniform current distribution. In an exemplary embodiment, currentdistribution improves with an increasing number of spokes, wherein thespokes provided on adjacent concentric wheels are substantially evenlyoffset.

Exemplary embodiments of electrical connectors are shown in FIGS. 26A,26B, 27A, and 27B. The current distribution across the exemplaryembodiments of FIGS. 26A and 26B are shown in FIGS. 26C and 26D (leftand right images, respectively). The current distribution across theexemplary embodiments of FIGS. 27A and 27B are shown in FIGS. 27C and27D (left and right images, respectively). The zone of reduced velocityproduced by each of the exemplary electrical connectors of FIGS. 26A,26B, 27A, and 27B are shown in the contour maps of FIGS. 28A-28D, whereFIG. 28A corresponds to the exemplary embodiment of FIG. 26A, FIG. 28Bcorresponds to the exemplary embodiment of FIG. 26B, FIG. 28Ccorresponds to the exemplary embodiment of FIG. 27A, and FIG. 28Dcorresponds to the exemplary embodiment of FIG. 27B. Each of theexemplary contour maps of FIGS. 26 and 28 were calculated for a sampleelectrolyte solution of seawater flowing at an average velocity of 2.0m/s.

In some embodiments, as shown in FIGS. 29A-29B, the electrical connector1240 may contain a feature to mate with the separator 1180. Thedimensions of the separator and electrical connector may be designedtaking into consideration the effect on the zone of reduced velocitythat the combination of elements may create. In some embodiments, theprojections of the separator can be collinear with one or more spokes ofthe electrical connector to reduce the zone of reduced velocity. Inother embodiments, the projections of the separator may be angularlyoffset from the spokes of the electrical connector. Additionally, duringoperation of an electrochemical cell, it is often desirable to keep theoperating temperature low even when a higher flow of electrical currentis passed to the electrochemical cell. Conventional electrochemicalcells typically include titanium only electrical connectors welded to atitanium outer shell. The titanium electrical connectors generallyprovide for a high degree of chemical resistance but may not be optimalfor providing current to the electrochemical cell without generatingundesirable amounts of heat (and wasted energy). Due to the highresistivity of titanium connectors, the current supplied to thetraditional titanium connector may have to be limited, so thetemperature rise of the connectors in air does not rise excessively.However this limits the output of product produced by theelectrochemical cell, as product generation is directly proportional tocurrent input. Because of the heat generation in traditional titaniumconnectors, the connectors cannot be totally enclosed in an electricallyinsulating material with a high Ingress Protection Level of IP54 orgreater. This arrangement ordinarily results in the requirement forexpensive electrical enclosures that do not trap heat as much as anencapsulated electrical connector. To overcome these problems,traditional titanium connectors are often made of larger cross-sectionmaterial which substantially increases the cost of electrical connectorand electrochemical cell.

The resistivity of copper is 1.707×10′ ohm-m while the resistivity oftitanium is 7.837×10′ ohm-m. Copper has nearly 46 times less electricalresistivity than titanium. Accordingly, in some embodiments theelectrical connector may be at least partially made of low-resistivitycopper. Copper, however, is more susceptible to chemical corrosion thantitanium and thus should be kept out of contact with electrolyte runningthrough an electrochemical cell.

In some embodiments, the electrical connector part in contact with theprocess fluid or electrolyte (for example, seawater containing corrosivetraces of equivalent chlorine), may be titanium. The heat generated byelectrical currents flowing through this material is efficiently removedby the flowing process fluid. As the self-cleaning flow velocity ofprocess fluid may be in excess of 2 m/s, the temperature rise in thetitanium part of the electrical connector is generally kept to anegligible value. The electrical connector part in contact with air maybe copper (or another metal or alloy having a lower resistivity thantitanium).

Air-liquid cooled electrical connectors including portions formed ofdifferent metals, for example, titanium and copper (or another metal oralloy having a lower resistivity than titanium) may overcome problemsexhibited by traditional titanium connectors. A lower electricallyresistant metal (e.g. copper) may form or be included in a portion ofthe electrical connector exposed to air. It is to be understood thatcopper is an example of a high conductivity material, and the electricalconnectors disclosed herein may substitute another high conductivitymaterial or alloy for copper. Thus, the terms “copper portion” and“copper” are used herein for convenience, but it is understood thatthese terms do not limit these elements to being formed of copper.

Due to the superior low electrical resistance of copper, the temperaturerise may be limited to a small and acceptable value. This outerconductor may be joined to the inner higher chemical resistant (forexample, titanium) part of the connector which is in contact withprocess liquid (for example, seawater). Due to the water-cooling effectof the process liquid, temperature rise of the inner higher chemicalresistant part (for example, titanium) of the connector can beeffectively limited to a small and acceptable value.

The overall dual metal electrical connector may be more cost efficientthan a traditional titanium-only connector for a comparable currentrating. The outer conductor of the dual metal electrical connector mayexhibit a low temperature rise and can be encapsulated in electricallyinsulating materials, thus removing the need for expensive electricalenclosures. Also, embodiments of the air-liquid cooled dual metalelectrical connector can provide for the supply of much higher currentto electrochemical cells being developed than would otherwise be thecase with traditional titanium only electrical cell connectors.

The titanium portion and the copper portion may be physically andelectrically connected within a flange of the electrochemical cell thatprovides a hermetic seal about the connector portions and seals theinterior of the electrochemical cell from the external environmentusing, for example, gaskets. In some embodiments the titanium portionmay be coupled to the copper portion by mechanical fasteners, forexample, bolts. The bolts 1420 may be formed from the same material asthe titanium portion or the copper portion. The titanium portion mayinclude arms or spokes that make electrical contact with one of anodesor cathodes in an electrochemical device and apertures to allow forprocess fluid, for example, electrolyte, to flow into or out of theelectrochemical device. The arms or spokes may include a feature, forexample, slots to facilitate engagement with electrodes in theelectrochemical device. The titanium portion may additionally oralternatively be coupled to the copper portion by an interference fit.The copper portion may extend from the titanium portion or maycompletely surround the titanium portion.

Additionally, the titanium portion may include a threaded outer rim thatmay be screwed into place in the copper portion by engagingcomplimentary threads on an inner rim of an aperture in the copperportion. The copper portion may include a lower cylindrical threadedportion that screws into an aperture in the titanium portion.

In a further embodiment, the copper portion may be replaced by apolymetallic electrical connector, for example, an alloy of titanium andcopper or one or more other high conductivity metals. The polymetallicelectrical connector may have a lower resistivity than titanium. Thepolymetallic electrical connector may be welded or otherwise physicallycontinuous with the titanium portion.

A solid central core element or fluid flow director may be provided toprevent fluid from flowing down the center tube of an electrochemicalcell and bypassing the gap. The core may be formed of a non-conductivematerial, for example, any one or more of PVC, PTFE, PVDF, ABS, HDPE, orother appropriate materials. The core may be mechanically unconnected tothe anode and cathode. In other embodiments, one or more mechanicalfasteners may be provided to fix the core in place and/or attach thecore to the housing or another element of the electrochemical cell, forexample, the electrode or end cap. In other embodiments, the core isheld in place within the innermost electrode by a friction fit. The coremay contact only a single one of the anode and cathode electrodes insome embodiments. One of the anode and cathode electrodes may beunconnected to and not contact the core.

In other embodiments, the central core element may be a conductivemember that is electrically coupled to one of the anode and cathodeelectrodes and may be utilized to deliver current to the one of theanode and cathode electrodes. In further embodiments, the central coreelement may include axial busbars and/or other conductive centralelements insulated from one another with a first axial busbar and/orother conductive central element electrically coupled to the anode and asecond axial busbar and/or other conductive central element electricallyinsulated from the first and electrically coupled to the cathode.

The electrochemical cell may include internal baffles. The baffles maybe utilized to control or modify the flow direction and/or mixing offluid passing through the electrochemical cell and may provideadditional path length to the fluid flow channels as compared to anelectrochemical cell in the absence of the baffles. Fluid flow throughthe electrochemical cell may be from inlet apertures to the fluidconduit or from the fluid conduit to the outlet apertures.

Electrochemical cells as disclosed herein may be included as part of alarger system. The system may be in some embodiments a sea-based system,for example, a ship or an oil rig, and in other embodiments a land basedbuilding, for example, a power plant, an oil drilling facility or systemor other industrial facility. In other embodiments, the system may be orinclude a swimming pool, or a treatment system for drinking water,wastewater, or industrial water treatment processes, that uses one ormore products of electrochemical devices, for example, a disinfectant totreat or disinfect water.

The system may include one or more electrochlorination systems that mayinclude one or more electrochemical or electrochlorination cells ordevices as disclosed herein. The system may include a source of anelectrolyte solution fluidly connectable to the electrochemical cell,for example, through the substantially centrally located aperture of theinlet end cap. The source of the electrolyte solution may be configuredto deliver the electrolyte solution at an average flow velocity throughthe fluid channel equal to or greater than the self-cleaning velocity asdisclosed herein. In some embodiments, the source of electrolytesolution is configured to deliver the solution at an average flowvelocity of about 2 m/s or greater.

The source of the electrolyte solution may include process liquid, whichin some embodiments is seawater, brine, or brackish water from sourcesexternal and/or internal to the system. For example, if the system is asea-based system, an external source may be the ocean and an internalsource may be, for example, a ballast tank in a ship. In a land basedsystem, an external source may be the ocean and an internal source maybe brackish wastewater from an industrial process performed in thesystem.

The system may be configured to produce a product compound from theelectrolyte solution and output a product solution comprising theproduct compound. The one or more electrochemical systems may producetreated or chlorinated water and/or a solution including, for example,sodium hypochlorite, from the water and distribute it to a point of use.The system may be fluidly connectable to a point of use, for example,through the substantially centrally located aperture of theelectrochemical cell outlet end cap. The point of use may include astorage vessel or distribution site. The point of use may be a source ofcooling water for the system, a source of disinfection agent for aballast tank of a ship, a downhole of an oil drilling system, or anyother system in which treated or chlorinated water may be useful. Thepoint of use may include a concentrating vessel, for example, for batchrecirculation of the product. Various pumps may control the flow offluid through the system. One or more sensors may monitor one or moreparameters of fluid flowing through the system, for example, ionicconcentration, chlorine concentration, temperature, or any otherparameter of interest.

The pumps and sensors may be in communication with a control system orcontroller which communicates with the sensors and pumps and controlsoperation of the pumps and other elements of the system to achievedesired operating parameters. The controller used for monitoring andcontrolling operation of the various elements of system may include acomputerized control system. The output devices may also comprisevalves, pumps, or switches which may be utilized to introduce productwater (e.g. brackish water or seawater) the source into theelectrochemical system or point of use and/or to control the speed ofpumps.

One or more sensors may also provide input to the computer system. Thesesensors may include, for example, sensors which may be, for example,flow sensors, pressure sensors, chemical concentration sensors,temperature sensors, or sensors for any other parameters of interest tosystem. These sensors may be located in any portion of the system wherethey would be useful, for example, upstream of point of use and/orelectrochemical system or in fluid communication with the source.

The system may include a plurality of electrochemical cells arranged inseries. In some embodiments, the system may contain between about 2 andabout 10 electrochemical cells arranged in series. The number ofelectrochemical cells in series may be selected as necessary to producea product compound having the required properties. Electrochemical cellsarranged in series may have components designed to minimize pressuredrop, as previously described. The effects of pressure drop oversubsequent electrochemical cells in series are generally cumulative.

In accordance with another aspect, there is provided a method ofoperating an electrochemical cell. The method may be used to operate oneor more electrochemical cells as disclosed herein. The method mayinclude introducing the electrolyte solution into the electrochemicalcell, for example through the substantially centrally located apertureof the inlet end cap, at a self-cleaning velocity as disclosed herein.The method may further include fluidly connecting a plurality ofelectrochemical cells and operating the electrochemical cells in series.In some embodiments, the method may include introducing the electrolytesolution at an average flow velocity through the fluid channel of about2 m/s or greater.

The method may include generating a product compound from theelectrolyte solution in the self-cleaning electrochemical cell. Togenerate the product compound, the electrochemical cell may be operatedby applying a voltage across the electrodes, for example, a voltagesufficient to generate the product compound. The voltage sufficient togenerate the product compound may generally depend on the composition ofthe electrolyte solution, the desired composition of the productcompound in a product solution, the average flow velocity through theelectrochemical cell, and a number of electrochemical cells operated inseries. In an exemplary embodiment, the electrodes are operated at aconstant current density and the average flow velocity is controlled toproduce the desired composition of the product compound. For example,the electrochemical cell may be operated at an average flow velocity ofbelow 10 m/s, below 6 m/s, below 3.5 m/s, below 3 m/s, or below 2.5 m/sas needed to generate a product of the desired composition. In the sameexemplary embodiment, a number of electrochemical cells may arranged inseries may be selected to generate the desired product, for example,less than 10, less than 8, less than 6, less than 4, or at least 2electrochemical cells may be arranged in series as needed.

The method may further comprise continuously operating theelectrochemical cells or system for a predetermined period of time. Aspreviously described, an electrochemical cell operated continuously atthe self-cleaning flow velocity may reduce scaling and thus the need foracid washing of the electrochemical cell. In some embodiments, theelectrochemical system may be continuously operated for at least 6months without scaling. Such an electrochemical system may becontinuously operated for 6, 12, 18, 24, or 36 months without scaling.

EXAMPLES Example 1: Pressure Drop Across Electrochemical Cell

The fluid conduit and cone of an electrochemical cell can be designed tominimize pressure drop across the electrochemical cell. In an exemplaryembodiment, CFD data was generated for inlet pressure across severalinlet fluid conduit dimensions. The data assumes an electrolyte solutionof seawater and an average flow velocity of 2 m/s, but other electrolytesolutions and their corresponding self-cleaning flow velocities may beused to obtain the desired conditions. The contour maps for the severalfluid conduit dimensions are shown in FIGS. 13A-13C. The exemplaryembodiment of FIG. 13A has a 20 mm linear region. The exemplaryembodiment of FIG. 13B has a 50 mm linear region, resulting in anaverage inlet pressure of 119 kPa. The exemplary embodiment of FIG. 13Chas a 75 mm linear region, resulting in an average inlet pressure of 117kPa. As can be shown from the figures, an increase to the lineartransition region has a concurrent reduction in pressure drop.

Additionally, CFD data was generated for several inlet cone angles at aconstant fluid conduit linear length (40 mm). The data is presented inthe velocity contour map of FIG. 14A and the graph of FIG. 14B. Therevolved angle of the cone relative to the centerline (i.e., half of theapex angle) was increased from 10 to 45 degrees and evaluated forpressure drop. The lowest pressure drop (about 18.8 kPa or 2.725 psi)was observed for the cone having an apex angle of 50°.

For an exemplary fluid conduit having a linear region of 40 mm, an inletcone apex angle of 50° minimizes the pressure drop across theelectrochemical cell. Similar conditions may be determined for otherfluid conduit and/or cone dimensions. Similar conditions may also bedetermined for other electrolyte solutions and/or average flowvelocities.

Example 2: Recirculation Effect Downstream from Separator and/orElectrical Connector

Scaling may develop where the average flow velocity of the electrolytesolution is below a threshold value. The separator may be designed tominimize regions of low flow velocity downstream, for example, by havingan aqualined configuration. As shown in the magnitude velocity contourmaps of FIGS. 30-31 , the flow velocity immediately downstream from astraight-edge separator approaches 0 m/s, which increases theprobability of scale occurring at this location. The arrows point in thedirection of flow and have a length indicating the magnitude of the flowvelocity. FIG. 30 shows the contour map of a side view of the fluidchannel, while FIG. 31 shows the contour map of a top view of the samefluid channel.

FIG. 32 is a magnitude velocity contour map of an aqualined separator.As shown in FIG. 32 , the downstream flow is more uniform and has asmaller velocity deviation from mean. The velocity deviation from meanfor the embodiment shown in FIG. 32 is plotted in the graph of FIG. 22 .Assuming an electrolyte solution of seawater and an average flowvelocity of 2 m/s, the percent velocity spread may cross the ±5% frommean threshold at about 100 mm flow distance (from the separator).

Thus, separators may be designed to create a more uniform downstreamflow having a smaller velocity deviation from mean to reduce scaling.Such a design may also reduce a length of the zone of reduced velocity,adding the capability to operate at a lower average flow velocity(requiring less energy) and reducing or eliminating the need for acidwashing of the electrochemical cell. Similar conditions may bedetermined for other electrolyte solutions and/or average flowvelocities.

Example 3: Flow Parameters within Electrochemical Cell

For flow in a pipe, Reynolds number is generally defined as:

${Re} = {\frac{\rho\;{uD}_{H}}{\mu} = {\frac{{uD}_{H}}{v} = \frac{{QD}_{H}}{vA}}}$

where:

D_(H) is hydraulic diameter of the pipe,

Q is volumetric flow rate (m³/s),

A is the pipe's cross-sectional area (m²),

u is the mean velocity of the fluid (m/s),

μ is the dynamic viscosity of the fluid (kg/(m*s),

ν is the kinematic viscosity (m²/s), and

ρ is the density of the fluid (kg/m³).

For an exemplary electrochemical cell having a plurality of fluidchannels, the Reynolds number for fluid flow through the flow areabetween the inlet cone and fluid conduit was determined to be 57,847.The approximate entrance length through such a conduit is about 380 mm.For fully-developed flow, turbulence tends to occur at a Reynolds numbergreater than about 2600. Thus, the flow through the fluid conduit ishighly turbulent.

For the same electrochemical cell, the Reynolds number for fluid flowthrough each of the concentric fluid channels was determined to be14,581. The approximate entrance length for the fluid channels is about70 mm. The flow through the fluid channels and downstream from theseparators resembles laminar flow.

These values assume an electrolyte solution of seawater at 20° C. and anaverage flow velocity of 2 m/s. Similar conditions may be determined forother electrolyte solutions and/or average flow velocities.

The phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. As used herein, theterm “plurality” refers to two or more items or components. The terms“comprising,” “including,” “carrying,” “having,” “containing,” and“involving,” whether in the written description or the claims and thelike, are open-ended terms, i.e., to mean “including but not limitedto.” Thus, the use of such terms is meant to encompass the items listedthereafter, and equivalents thereof, as well as additional items. Onlythe transitional phrases “consisting of” and “consisting essentiallyof,” are closed or semi-closed transitional phrases, respectively, withrespect to the claims. Use of ordinal terms such as “first,” “second,”“third,” and the like in the claims to modify a claim element does notby itself connote any priority, precedence, or order of one claimelement over another or the temporal order in which acts of a method areperformed, but are used merely as labels to distinguish one claimelement having a certain name from another element having a same name(but for use of the ordinal term) to distinguish the claim elements.

Having thus described several aspects of at least one embodiment, it isto be appreciated various alterations, modifications, and improvementswill readily occur to those skilled in the art. Any feature described inany embodiment may be included in or substituted for any feature of anyother embodiment. Such alterations, modifications, and improvements areintended to be part of this disclosure, and are intended to be withinthe scope of the invention. Accordingly, the foregoing description anddrawings are by way of example only.

What is claimed is:
 1. A self-cleaning electrochemical cell comprising:a cathode and an anode disposed concentrically in a housing about acentral axis of the housing; a fluid channel defined between the cathodeand the anode and extending substantially parallel to the central axis;and a separator residing between the cathode and the anode andconfigured to maintain the fluid channel, the separator including aprojection having a height which maintains a width of the fluid channel,the projection having a length dimension parallel to the central axis ofthe housing, the projection increasing in width along a length of theprojection from a first lengthwise end to a lengthwise position betweenthe first lengthwise end and a second lengthwise end of the projectionand decreasing in width along the length of the projection from thelengthwise position to the second lengthwise end, the separatorconfigured to maintain a zone of reduced velocity within the fluidchannel downstream of the separator to be less than a predeterminedlength, and the separator configured to maintain an electrolyte solutionvelocity deviation from mean to be within ±18% of an average flowvelocity of the electrolyte solution through the fluid channel.
 2. Theself-cleaning electrochemical cell of claim 1, wherein the velocitydeviation from mean at the predetermined length is less than ±5% of theaverage flow velocity of the electrolyte solution.
 3. The self-cleaningelectrochemical cell of claim 2, wherein the velocity deviation frommean at the predetermined length is less than ±2% of the average flowvelocity of the electrolyte solution.
 4. The self-cleaningelectrochemical cell of claim 1, wherein the predetermined length isless than about 120 mm for seawater flowing through the fluid channel atan average flow velocity of between 2 and 2.5 m/s.
 5. The self-cleaningelectrochemical cell of claim 4, wherein the predetermined length isless than about 60 mm.
 6. The self-cleaning electrochemical cell ofclaim 1, wherein the separator comprises a ring and a plurality ofprojections extending from the ring, each projection having a heightcorresponding to the width of the fluid channel.
 7. The self-cleaningelectrochemical cell of claim 6, wherein a number of projections and thelength and width of each projection is selected to maintain the zone ofreduced velocity at less than the predetermined length.
 8. Theself-cleaning electrochemical cell of claim 1, including a plurality ofcathodes and a plurality of anodes arranged concentrically about thecentral axis of the housing and a respective one of a plurality of fluidchannels being defined between each adjacent cathode and anode, eachfluid channel extending substantially parallel to the central axis. 9.The self-cleaning electrochemical cell of claim 8, including a pluralityof separators, each separator configured to maintain a respective one ofthe plurality of fluid channels, the plurality of separators eachincluding a ring and a plurality of projections extending from the ring.10. The self-cleaning electrochemical cell of claim 1, wherein theseparator is configured to mate with at least one of the cathode and theanode.
 11. A system comprising: the self-cleaning electrochemical cellof claim 1 having an inlet and an outlet in fluid communication with thefluid channel; and a source of the electrolyte solution having an outletfluidly connectable to the inlet of the self-cleaning electrochemicalcell and configured to deliver the electrolyte solution at an averageflow velocity through the fluid channel of 2 m/s or greater, theself-cleaning electrochemical cell configured to produce a productcompound from the electrolyte solution and to output a product solutioncomprising the product compound, the self-cleaning electrochemical cellbeing fluidly connectable to a point of use through the outlet.
 12. Thesystem of claim 11, wherein the source of the electrolyte solutioncomprises at least one of seawater, brackish water, and brine.
 13. Thesystem of claim 11, including a plurality of self-cleaningelectrochemical cells arranged in series.